Dolphins' biggest key to success

The key to success for any NFL franchise is the quarterback position -- and that could not be any more fitting for the Miami Dolphins.

Starting quarterback Ryan Tannehill remains a mystery in South Florida. While other quarterbacks in his 2012 draft class have led their teams to the playoffs (Robert Griffin III, Andrew Luck) and won a Super Bowl (Russell Wilson), Tannehill is just 15-17 as a starter and has yet to post a winning season.

Tannehill has stayed in that middle ground in two seasons. He has done enough to make the Dolphins believe in his potential but has yet to take the Dolphins over the hump. He set career highs last year with 3,913 yards, 24 touchdowns and an 81.7 passer rating. This is a huge Year 3 for Tannehill to prove he can be a franchise building block. Otherwise, the Dolphins may have to go in another direction in 2015, and that could set the franchise back another couple of years. It's also important to note that third-year head coach Joe Philbin is also on the hot seat this year.

The Dolphins have approximately $16 million in salary-cap room heading into training camp. That's a sizable amount, and Miami will most likely take much of that into next season.

A big reason the Dolphins have cap space is they are not spending an enormous amount of money on quarterbacks. Tannehill, the No. 8 overall pick in 2012, is in the third year of his rookie contract. Other teams have doled out contracts of $100 million or more, with per-season salaries ranging from $14 million to $20 million.

At some point, the Dolphins will have to pay the going rate for a franchise quarterback when they find one. But is Tannehill a franchise quarterback? Will Miami have to pay Tannehill around $15 million per season for the long haul? Those things will be dictated by Tannehill's play over the next season or two.